The enzymes responsible for dextran synthesis by a cariogenic microorganism (Strep mutans) have been extensively purified and a fraction which synthesizes insoluble dextran only has been isolated. These enzymes have been studied by isoelectric focusing. The transphosphorylase activity associated with microtubular protein has been studied and it has been established that this enzyme does not react with N-site nucleotide. A new reaction which augments the amount of E-site GTP in a time dependent process has been discovered.